The present invention relates to perpendicular magnetic recording media, and more particularly relates to media designed to suppress soft magnetic underlayer noise.
Perpendicular magnetic recording systems have been developed for use in computer hard disk drives. Some examples of perpendicular magnetic recording heads for use in such systems are described in U.S. Pat. No. 4,438,471 to Oshiki et al., U.S. Pat. No. 4,541,026 to Bonin et al., U.S. Pat. No. 4,546,398 to Toda et al., U.S. Pat. No. 4,575,777 to Hosokawa, U.S. Pat. No. 4,613,918 to Kania et al., U.S. Pat. No. 4,649,449 to Sawada et al, U.S. Pat. No. 4,731,157 to Lazzari, and U.S. Pat. No. 4,974,110 to Kanamine et al.
Some examples of perpendicular magnetic recording media are described in U.S. Pat. No. 4,410,603 to Yamamori et al., U.S. Pat. No. 4,629,660 to Sagoi et al., U.S. Pat. No. 5,738,927 to Nakamura et al., and U.S. Pat. No. 5,942,342 to Hikosaka et al.
One of the challenges to implement perpendicular recording is to resolve the problem of soft underlayer noise. The noise is caused by fringing fields generated by magnetic domains in the soft underlayer that can be sensed by the reader. For the write process to be efficient, high moment materials, e.g., BS greater than 20 kG, may be used for the soft underlayer. If the domain distribution of such materials is not carefully controlled, very large fringing fields can introduce substantial amounts of noise in the read element. Not only can the reader sense the steady-state distribution of magnetization in the soft underlayer, but it can also affect the distribution of magnetization in the soft underlayer, thus generating time-dependent noise. Both types of noise should be minimized.
The present invention has been developed in view of the foregoing, and to address other deficiencies of the prior art.
The present invention provides perpendicular recording media having a soft magnetic underlayer and magnetic regions which generate an external magnetic field in the soft magnetic underlayer. The soft magnetic underlayer is brought into a substantially single-domain state by the magnetic field. Reducing or eliminating multiple domains addresses the noise problem noted above. In a preferred embodiment, the magnetization in such a single-domain state is aligned radially without local domain walls. It is noted that a xe2x80x9csingle-domainxe2x80x9d state is an approximation, which applies to materials without any magnetic defects. In actual magnetic films, the film will be magnetically saturated in accordance with the present invention in order to sufficiently reduce the number of domain walls, thus suppressing soft underlayer noise.
An aspect of the present invention is to provide a perpendicular magnetic recording medium including a soft magnetic underlayer and means for generating a magnetic field in the soft magnetic underlayer.
Another aspect of the present invention is to provide a perpendicular magnetic recording medium which includes a soft magnetic underlayer, a hard magnetic recording layer over the soft magnetic underlayer, and at least one magnetic region which generates a magnetic field in the soft magnetic underlayer.
A further aspect of the present invention is to provide a method of making a perpendicular magnetic recording medium. The method includes the steps of providing at least one magnetic region on a substrate disk, and providing a soft magnetic underlayer and a hard magnetic recording layer on the substrate disk in proximity to the at least one magnetic region. The magnetic region generates a magnetic field in the soft magnetic underlayer.
These and other aspects of the present invention will be more apparent from the following description.